Winter moth numbers on Cape Cod fall thanks to parasitic flies

Friday

Sep 14, 2018 at 7:03 AMSep 14, 2018 at 7:20 AM

With the help of a parasitic fly, Massachusetts scientists have declared victory over the ever-invasive caterpillars of winter moths.

Winter moth larva, which is especially fond of eating tree leaves, blueberry crops and orchards, has been responsible for the defoliation of tens of thousands of acres along the New England coast each year since the early 2000s, and has hit some parts of Cape Cod especially hard.

Entomologists at the University of Massachusetts Amherst now say the winter-moth population is decreasing to non-pest levels thanks largely to the introduction of a parasitic fly native to Europe. The pest-reduction approach, known as “biological control,” is expected to save Massachusetts residents millions of dollars in future pesticide costs, according to researchers.

“After 14 years of effort, we have successfully converted winter moth, a major defoliation invading Eastern New England, into a non-pest, presumably on a permanent basis,” said Joseph Elkinton, an entomologist at UMass Amherst, in a statement. “We have averted what was shaping up to be another major invasion calamity for the entire United States comparable to gypsy moth.”

Larry Dapsis, entomologist with the Cape Cod Cooperative Extension, says the parasitic flies were released in four locations on Cape Cod and the results have been dramatic. He said hardly any winter moths were found last winter and the prediction is for no problem this year.

"We examined blueberry fields and we never found a winter moth larva in a bud," Dapsis said. He predicted spraying against winter moths on Cape Cod will not be necessary again.

Dapsis said the results mirror those seen in Atlantic Canada where the winter moth problem had been especially severe.

"This is a stunning example of how the good guys can overtake the bad guys without the use of chemicals," Dapsis said.

Elkinton, along with fellow entomologists George Boettner and Hannah Broadley, has been working toward this goal for years. In 2005, the group started collecting the flies, which prey specifically on the winter moth, and grew them in a controlled UMass lab.

The flies were then released at 44 separate sites along the Massachusetts coast earlier this year, and the researchers have verified the flies have successfully populated in at least 38 of the locations.

Elkinton said the biological approach, which is common in fighting invasive pests around the world, is working especially well here.

″[It’s] quite rare, at least on forest trees,” he said. “In fact, I can’t think of any other example involving a major forest insect in North America.”

The flies do not prey on anything besides the winter moth, according to the researchers. And while the approach will not wipe out the winter moth entirely, it will greatly reduce the invasive species.

“The object of biological control is to reduce density of the invasive species to non-pest status,” Elkinton said. “That is what we believe we have achieved.”

Eli Sherman is an investigative and in-depth reporter at Wicked Local and GateHouse Media. Email him at esherman@wickedlocal.com, or follow him on Twitter @Eli_Sherman.